This invention relates to reciprocable piston pumps for pumping liquids; more particularly, the invention relates to a priming piston attachment for a reciprocable pump which is particularly useful for pumping high viscosity materials.
Reciprocable pumps have long been used for pumping liquids of various viscosities where the pump is typically at least partially immersed into a liquid container to withdraw liquid from the container and pump it under pressure via a delivery hose to a remote point. On the piston upstroke, liquid is drawn into an intake valve housing through an intake valve which is typically located at the bottom of the pump. At the same time, liquid is forced out of the main pumping cylinder by the upward movement of the piston. On the downstroke, the intake valve closes on a seat and a piston valve opens to permit liquid in the intake valve housing to flow upwardly into the main pump cylinder above the piston. At the same time, the pump displacement rod is moving down into the main pump cylinder forcing liquid out through the outlet housing.
When high-viscosity liquids are pumped by a reciprocable pump, it frequently becomes necessary to increase the force applied against the liquid in the container to assist in moving the liquid into the pump intake valve housing. Inductor plates or ram plates are frequently used for this purpose, wherein an external force is applied against the liquid surface to develop a positive pressure to force the liquid upwardly into the pump intake valve housing. Another technique which has been used is to add a priming cylinder to the lower end of the pump, beneath the intake valve housing, and to add a priming piston and rod extension to the reciprocable pump rod so that the priming piston can reciprocate into and out of the priming cylinder. Under this circumstance, the priming piston also moves upwardly during the pump upstroke and forces liquid into the priming cylinder and thereafter upwardly into the intake valve housing. During the downstroke the priming piston is pushed completely out of the priming cylinder to open the bottom of the cylinder into contact with the liquid in the container.
In pumping highly viscous materials such as sealants, adhesives and silicones, there is a need to further enhance the flow of liquids into the pump to minimize or avoid pump cavitation. In particular, there is a need to improve the flow of liquid into the priming cylinder during the pump downstroke to enable the priming cylinder to completely fill with liquid for delivery during the pump upstroke.